An integrated circuit (“IC”) is a semiconductor device that includes many electronic components (e.g., transistors, diodes, inverters, etc.) manufactured on a small semiconductor die. These electrical components are interconnected to form larger scale circuit components (e.g., gates, cells, memory units, arithmetic units, controllers, decoders, etc.) on the IC. The electronic and circuit components of IC's are jointly referred to below as “components.”
An integrated circuit also includes multiple layers of metal and/or polysilicon wiring that interconnect the various electronic and circuit components. For instance, many integrated circuits are currently fabricated with five metal layers. Most integrated circuits use the “Manhattan” wiring model, which specifies alternating layers of preferred-direction horizontal and vertical wiring. (Viewed from above, the horizontal and vertical wiring resemble the orthogonal streets of Manhattan.) In the Manhattan wiring model, essentially all of the interconnect wires are horizontal or vertical.
To connect electrical wiring on different metal layers, a “via” is used. A via is essentially a metal and/or polysilicon column that connects wiring on two different metal layers. Vias are generally created slightly larger than the wiring that will be connected in order to account for any misalignment between different semiconductor layers. In traditional Manhattan-wired semiconductors, the vias are designed as square geometric structures when viewed from above.
In order to reduce the amount of area on an integrated circuit dedicated to wiring and reduce the length (and thus propagation delay) of individual wires diagonal wiring systems have been introduced. In an integrated circuit that uses diagonal wiring, two pins that are separated by both a large vertical and horizontal distance from each other (using the Manhattan grid as a reference) can be coupled with a diagonal wire that is shorter that the sum of horizontal wire and a vertical wire that would be required in a Manhattan routed integrated circuit.
Diagonal wiring has proven to be a method creating smaller integrated circuit designs. Due to the reduced size, the yields on diagonally wired integrated circuits may be better than similar but larger Manhattan wired integrated circuits. Furthermore, since diagonally wired integrated circuits have shorter wiring runs, diagonally wired integrated circuits may operate at higher speeds.
As previously set forth, interconnect wires on different metal layers are traditionally connected together with square vias. However, square vias may not prove to be optimal for a diagonally wired integrated circuit. For example, the corners of a square shaped via do not provide much help in connecting wires those comers may cause design rule violations by being too close to nearby diagonal wires. It would therefore be desirable to determine how to best design and manufacture vias for a diagonally wired integrated circuit.